More Information

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Filter preamps work like a classic tone control, rolling off high frequencies as you turn the knob down. But they do a lot more: Near the point you set for the cutoff frequency, there is a boost in the signal level that can be used like a sweepable EQ. With multiple pickups, a separate filter can be used on each pickup before the signals are blended, giving you tones that are not possible with a conventional preamp and single outboard amp. With the Underhill system, filters can also be combined with EQ modules to make unique systems with more layers of control. Contact us to discuss your ideas and get a price quote.

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The latest Underhill filters feature a new design with fully adjustable boost levels on all models. They are the highest-performance onboard filters available, with the following features (click on a system above to see detailed specs):

• Resonant boost level adjustable from 0-13dB on all filters.

• Significantly lower noise than other filters.

• More headroom: Most pickups and gain settings are easily handled at 7-8V (a worn 9V battery).

• Precise controls: The frequency, resonance, and gain are consistent at any settings.

• Low power: Power consumption is lower than previous Underhill preamps.

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Four filter models are available for different control layouts:

• FV Variable Q Filter (Stacked frequency and Q knobs).

• FP Push-Pull Q Filter (Single push-pull frequency knob).

• FS Switched Q Filter (Single frequency knob and 3-way Q switch).

• FT Treble Boost Filter (Engage with volume push-pull or separate SB mini switch.)

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Input buffer modules are available which allow different types of pickups to be mixed and matched:

• BP Buffer - For passive and most active pickups.

• BA Buffer - For high-output active pickups.

• B4 Buffer - For four-string multi-coil pickups.

• B5 Buffer - For five-string multi-coil pickups.

• BZ Buffer - For piezo pickups.

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For detailed information on these modules, go to the Preamp Modules page, and click on the module.